U.S. patent application number 17/513766 was filed with the patent office on 2022-05-05 for liquid metal-based flexible electronic device and preparation method and use thereof.
The applicant listed for this patent is Harbin Institute of Technology, Shenzhen. Invention is credited to Huanhuan FENG, Liang FENG, Yaming LIU, Xing MA, Li WANG, Min WANG, Jiaheng ZHANG, Yueyue ZHANG, Zhenchao ZHANG, Weiwei ZHAO.
Application Number | 20220141963 17/513766 |
Document ID | / |
Family ID | 1000005987850 |
Filed Date | 2022-05-05 |
United States Patent
Application |
20220141963 |
Kind Code |
A1 |
FENG; Liang ; et
al. |
May 5, 2022 |
LIQUID METAL-BASED FLEXIBLE ELECTRONIC DEVICE AND PREPARATION
METHOD AND USE THEREOF
Abstract
A liquid metal-based flexible electron device and a preparation
method are disclosed. In the method, 3D printing and the
characteristic that ABS plastic can be dissolved by acetone are
utilized, and a microchannel is quickly constructed in the flexible
substrate of Ecoflex, and liquid metal is then injected into the
microchannel to complete the manufacturing of a flexible electronic
device. The gold film on the surface of ABS is transferred to the
surface of the flexible Ecoflex substrate.
Inventors: |
FENG; Liang; (Shenzhen City,
CN) ; LIU; Yaming; (Shenzhen City, CN) ; FENG;
Huanhuan; (Shenzhen City, CN) ; WANG; Li;
(Shenzhen City, CN) ; ZHANG; Yueyue; (Shenzhen
City, CN) ; ZHANG; Zhenchao; (Shenzhen City, CN)
; WANG; Min; (Shenzhen City, CN) ; ZHAO;
Weiwei; (Shenzhen City, CN) ; MA; Xing;
(Shenzhen City, CN) ; ZHANG; Jiaheng; (Shenzhen
City, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Harbin Institute of Technology, Shenzhen |
Shenzhen City |
|
CN |
|
|
Family ID: |
1000005987850 |
Appl. No.: |
17/513766 |
Filed: |
October 28, 2021 |
Current U.S.
Class: |
29/849 |
Current CPC
Class: |
B29C 64/30 20170801;
H05K 3/103 20130101; B29K 2055/02 20130101; H05K 3/16 20130101;
H05K 3/107 20130101; B33Y 80/00 20141201; C23C 14/205 20130101;
H05K 2203/1305 20130101; B33Y 40/20 20200101; B29L 2031/34
20130101 |
International
Class: |
H05K 3/10 20060101
H05K003/10; H05K 3/16 20060101 H05K003/16; C23C 14/20 20060101
C23C014/20; B33Y 40/20 20060101 B33Y040/20; B29C 64/30 20060101
B29C064/30 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 30, 2020 |
CN |
202011187023.X |
Claims
1. A method for preparing a liquid metal-based flexible electronic
device, comprising preparing an ABS plastic model by a 3D printing
according to a circuit pattern; performing an ion sputtering on a
surface of the ABS plastic model to form a gold film, to obtain a
gold-plated ABS circuit; introducing Ecoflex into a mold,
suspending the gold-plated ABS circuit inside the mold such that
the gold-plated ABS circuit does not contact the mold, and curing
Ecoflex to obtain a cured model; immersing the cured model in
acetone to dissolve the ABS plastic model, to obtain a microchannel
with a gold plating on an inner wall of the microchannel in Ecoflex
substrate; and injecting a gallium-indium eutectic into the
microchannel with a gold plating on the inner wall, inserting a
copper wire into the liquid metal at both ends of the microchannel
with a gold plating on the inner wall, and applying Ecoflex to a
port of the microchannel with a gold plating on the inner wall and
curing Ecoflex such that the circuit is encapsulated, to obtain the
liquid metal-based flexible electronic device.
2. The method as claimed in claim 1, wherein the ion sputtering is
performed for 60-100 s.
3. The method as claimed in claim 1, wherein curing Ecoflex is
performed independently for 2 to 4 hours.
4. The method as claimed in claim 1, wherein immersing the cured
model in acetone is performed for 12-24 hours.
5. The method as claimed in claim 1, wherein the gallium-indium
eutectic has a Ga content of 74.5 wt %, and an In content of 25.5
wt %.
6. The method as claimed in claim 1, wherein the copper wire has a
length of 50-70 mm.
7. A liquid metal-based flexible electronic device, which is
prepared by the method as claimed in claim 1.
Description
[0001] This application claims the benefit and priority of Chinese
Patent Application No. 202011187023.X, entitled "Liquid
metal-containing flexible electronic device and preparation method
and use thereof" filed with the Chinese National Intellectual
Property Administration on Oct. 30, 2020, the disclosure of which
is incorporated by reference herein in its entirety as part of the
present application.
FIELD OF THE INVENTION
[0002] The present disclosure relates to the technical field of
liquid metal-based flexible electronic device, and particularly to
a liquid metal-based flexible electronic device and a preparation
method and use thereof.
BACKGROUND
[0003] The background description includes information that may be
useful in understanding the present invention. It is not an
admission that any of the information provided herein is prior art
or relevant to the presently claimed invention, or that any
publication specifically or implicitly referenced is prior art.
[0004] Liquid metals, such as gallium-based and bismuth-based
alloys, are a large class of emerging functional materials with
unique physical and chemical properties. They are liquid at room
temperature and have the properties of high boiling point, strong
conductivity, high thermal conductivity, no needs of
high-temperature smelting in their manufacturing process,
environmental friendliness, and nontoxicity, and meanwhile low
melting point which is not for conventional high melting point
metal materials. Its molding ability in molten state creates
conditions for quickly building different forms of functional
devices, and it is very suitable for the manufacturing flexible
electronic devices.
[0005] At present, the methods for preparing flexible electronic
devices based on liquid metal mainly include (1) direct writing
method: using a syringe or similar suction tools to extract a
liquid metal ink, slowly injecting liquid metal into a clean empty
refill, writing and drawing a circuit pattern on a substrate; (2)
plane printing method: on the basis of direct writing method, in
combination with a complete equipment which is composed of moving
guide rail, digitally controlled module, print head and setting
module, charging the liquid metal ink to the print head, performing
a fast printing of electronic patterns on the substrate according
to the control instructions issued by computer software; (3) ink
jet printing method: placing liquid metal in an inkjet pen, in
which, the liquid metal enters a nozzle from a container under the
action of gravity, and spraying liquid metal out of the nozzle
under the action of annular columnar air, and transferring a
designed circuit pattern to the substrate through a mask of
specific shape; (4) lithography: constructing a microchannel in the
flexible substrate through lithography and other technologies, and
making the circuit by injecting liquid metal into the microchannel
through injection operation; (5) 3D (three-dimensional) printing
method: printing a constructed object layer by layer and depositing
a flexible substrate, a liquid metal ink, a flexible substrate in
turn, which could avoid corrosion and contribute to environmental
protection.
[0006] Direct writing, planar printing, and inkjet printing method
could only construct traditional two-dimensional circuits. These
two-dimensional circuits are formed by liquid metal films. When
carrying high current density, fracture problems may be caused by
the electromigration phenomenon. The construction of microchannels
by lithography is cumbersome and costly, which is not suitable for
large-scale application and promotion. The direct printing of
flexible circuits with a 3D metal printer simplifies the
manufacturing process and saves materials, but the cost of this 3D
metal printer is still high.
SUMMARY OF THE INVENTION
[0007] In view of this, an object of the present disclosure is to
provide a liquid metal-based flexible electron device and a
preparation method thereof. According to the method of the present
disclosure, a microchannel is quickly constructed in a flexible
Ecoflex (silica gel) substrate, and a liquid metal is then injected
into the microchannel, and thereby a flexible electronic device is
fabricated, without the construction of microchannel(s) by
traditional lithography process(es), which greatly simplifies the
operations and reduces the cost.
[0008] In order to achieve the above object of the present
disclosure, the present disclosure provides the following technical
solutions:
[0009] The present disclosure provides a method for preparing a
liquid metal-based flexible electronic device, comprising:
preparing an ABS (Acrylonitrile Butadiene Styrene) plastic model by
a 3D printing according to a circuit pattern; performing an ion
sputtering on a surface of the ABS plastic model to form a gold
film, to obtain a gold-plated ABS circuit; introducing Ecoflex into
a mold, suspending the gold-plated ABS circuit inside the mold such
that the gold-plated ABS circuit does not contact the mold, and
curing Ecoflex, to obtain a cured model; immersing the cured model
in acetone to dissolve the ABS plastic model, to obtain a
microchannel with a gold plating on an inner wall of the
microchannel in the Ecoflex substrate; and injecting a
gallium-indium eutectic into the microchannel with a gold plating
on the inner wall, inserting a copper wire into the liquid metal at
both ends of the microchannel with a gold plating on the inner
wall, and applying Ecoflex to a port of the microchannel with a
gold plating on the inner wall and curing Ecoflex such that the
circuit is encapsulated, to obtain the liquid metal-based flexible
electronic device.
[0010] In some embodiments, the ion sputtering is performed for
60-100 s.
[0011] In some embodiments, curing Ecoflex is performed
independently for 2 to 4 hours.
[0012] In some embodiments, immersing the cured model in acetone is
performed for 12-24 hours.
[0013] In some embodiments, the gallium-indium eutectic has a Ga
content of 74.5 wt %, and an In content of 25.5 wt %.
[0014] In some embodiments, the copper wire has a length of 50-70
mm.
[0015] The present disclosure also provides a liquid metal-based
flexible electronic device, which is prepared by the method as
described in the above technical solutions.
[0016] The present disclosure also provides use of the liquid
metal-based flexible electronic device as described in the above
technical solutions in the fields of smart furniture, smart wear,
electronic skin, flexible sensing, radio frequency antennas,
biomedicine, and aerospace.
[0017] The present disclosure provides a method for preparing a
liquid metal-based flexible electron device, comprising the
following steps: preparing an ABS plastic model by a 3D printing
according to a circuit pattern; performing an ion sputtering on a
surface of the ABS plastic model to form a gold film, to obtain a
gold-plated ABS circuit; introducing Ecoflex into a mold,
suspending the gold-plated ABS circuit inside the mold such that
the gold-plated ABS circuit does not contact the mold, and curing
Ecoflex, to obtain a cured model; immersing the cured model in
acetone to dissolve the ABS plastic model, to obtain a microchannel
with a gold plating on an inner wall of the microchannel in the
Ecoflex substrate; injecting a gallium-indium eutectic into the
microchannel with a gold plating on the inner wall, inserting a
copper wire into the liquid metal at both ends of the microchannel
with a gold plating on the inner wall, and applying Ecoflex to a
port of the microchannel with a gold plating on the inner wall and
curing Ecoflex such that the circuit is encapsulated, to obtain the
liquid metal-based flexible electronic device. In the present
disclosure, 3D printing and the characteristic that ABS plastic can
be dissolved by acetone were utilized, and a microchannel is
quickly constructed in the flexible substrate of Ecoflex, and
liquid metal is then injected into the microchannel to complete the
manufacturing of a flexible electronic device. In the inventive
method, the construction of the microchannel by a traditional
lithography process is not needed, which could greatly simplify the
operation steps and reduce the cost.
[0018] The present disclosure also provides a liquid metal-based
flexible electron device prepared by the method as described in the
above technical solutions. In present disclosure, the gold film on
the surface of ABS is transferred to the surface of a flexible
Ecoflex substrate, which improves the wettability of liquid metal
within the microchannel, thereby facilitating the subsequent liquid
metal-injection operation. The prepared flexible liquid metal
circuit has high elasticity, and could meet the needs of various
deformations, and has stable electrical properties during
service.
[0019] The adhesion work of microchannels at different stages was
calculated according to the Young Dupre equation. The adhesion work
after plating gold increases from 110 mJ/m.sup.2 (before plating
gold) to 200 mJ/m.sup.2, which is increased by nearly twice,
thereby significantly improving the wettability. The obtained
liquid metal-based flexible electronic devices could be stretched
to a strain of 600%, bent 180.degree., and twisted 360.degree., and
when being subjected to 1,000-cycle tensile tests with a strain of
100%, exhibit stable peaks and valleys in the resistance curve.
[0020] Various objects, features, aspects and advantages of the
inventive subject matter will become more apparent from the
following detailed description of preferred embodiments, along with
the accompanying drawing figures in which like numerals represent
like components.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 shows a flowchart of the method for preparing the
liquid metal-based flexible electron device according to one
embodiment of the present disclosure.
[0022] FIGS. 2A-2B show shapes and structures of the liquid
metal-based flexible electron devices obtained in Example 1 and
Comparative Example.
[0023] FIG. 3 shows a summary of peaks and troughs after 1,000
cycles (with a strain of 100%) of the liquid metal-based flexible
electronic devices prepared in Example 1.
[0024] FIGS. 4A-4B show resistance curves of the liquid metal-based
flexible electronic devices prepared in Example 1 and Comparative
example in a tensile cycle with a strain of 600%, FIG. 4A for
Comparative Example and FIG. 4B for Example 1.
[0025] FIGS. 5A-5E show resistance curves of the liquid metal-based
flexible electronic devices with different microchannel sizes
prepared in Example 1 in a tensile cycle, FIG. 5A for 0.4 mm, FIG.
5B for 0.6 mm, FIG. 5C for 0.8 mm, FIG. 5D for 1.0 mm, and FIG. 5E
for 1.2 mm.
[0026] FIG. 6 shows the curve of peak resistances of the liquid
metal-based flexible electronic devices with different microchannel
sizes prepared in Example 1 versus strains.
[0027] FIG. 7 shows a summary of resistance curves of the liquid
metal-based flexible electronic device with a microchannel 1.2 mm
in size, as prepared in Example 1, in a single tensile of each
strain.
[0028] FIG. 8 shows curves of circuit resistance of the liquid
metal-based flexible electronic devices with different microchannel
sizes as prepared in Example 1 versus the bending angle.
[0029] FIG. 9 shows curves of the circuit resistance of the liquid
metal-based flexible electronic devices with different microchannel
sizes as prepared in Example 1 versus the twisting angle.
[0030] FIG. 10 shows slopes of the variation curve of the liquid
metal-based flexible electronic devices with different microchannel
sizes as prepared in Example 1.
[0031] FIG. 11 shows a schematic diagram of the circuit voltage
test.
[0032] FIGS. 12A-12C show three circuit patterns of different
complexity.
[0033] FIGS. 13A-13C show variations of circuit resistance versus
the mass of weights when the liquid metal-based flexible electronic
devices with different microchannel sizes prepared in Example 1 are
configured in the simple-pattern circuit with Ecoflex of different
thicknesses, FIG. 13A for 0.4 mm, FIG. 13B for 0.7 mm, and FIG. 13C
for 1.0 mm.
[0034] FIGS. 14A-14C show variations of circuit resistance versus
the mass of weights when the liquid metal-based flexible electronic
devices with different microchannel sizes prepared in Example 1 are
configured in the complex-pattern circuit with Ecoflex of different
thicknesses, FIG. 14A for 0.4 mm, FIG. 14B for 0.7 mm, and FIG. 14C
for 1.0 mm.
[0035] FIGS. 15A-15C show variations of circuit resistance versus
the mass of weights when the liquid metal-based flexible electronic
devices with different microchannel sizes prepared in Example 1 are
configured in the more complex-pattern circuit with Ecoflex of
different thicknesses, FIG. 15A for 0.4 mm, FIG. 15B for 0.7 mm,
and FIG. 15C for 1.0 mm.
[0036] FIG. 16 shows experimental results of controlling the
brightness of the bulb by stretching the liquid metal-based
flexible electronic devices with different microchannel sizes as
prepared in Example 1, panel a) for 0.4 mm, panel b) for 0.6 mm,
panel c) for 0.8 mm, panel d) for 1.0 mm, and panel e) for 1.2
mm.
[0037] FIG. 17 shows experimental results of controlling the
brightness of the bulb by bending or twisting the liquid
metal-based flexible electronic devices with different microchannel
sizes as prepared in Example 1, panel a) for 0.4 mm, panel b) for
0.6 mm, panel c) for 0.8 mm, panel d) for 1.0 mm, and panel e) for
1.2 mm.
[0038] FIGS. 18A-18B show curve diagrams of human pulse measured
before and after exercise, FIG. 18A of which represents before
exercise; FIG. 18B of which represents after exercise.
DETAILED DESCRIPTION
[0039] The following discussion provides example embodiments of the
inventive subject matter. Although each embodiment represents a
single combination of inventive elements, the inventive subject
matter is considered to include all possible combinations of the
disclosed elements. Thus if one embodiment comprises elements A, B,
and C, and a second embodiment comprises elements B and D, then the
inventive subject matter is also considered to include other
remaining combinations of A, B, C, or D, even if not explicitly
disclosed.
[0040] As used in the description herein and throughout the claims
that follow, the meaning of "a," "an," and "the" includes plural
reference unless the context clearly dictates otherwise. Also, as
used in the description herein, the meaning of "in" includes "in"
and "on" unless the context clearly dictates otherwise.
[0041] The present disclosure provides a method for preparing a
liquid metal-based flexible electron device, comprising the
following steps: preparing an ABS plastic model by a 3D printing
according to a circuit pattern; performing an ion sputtering on a
surface of the ABS plastic model to form a gold film, to obtain a
gold-plated ABS circuit; introducing Ecoflex into a mold,
suspending the gold-plated ABS circuit inside the mold such that
the gold-plated ABS circuit does not contact the mold, and curing
Ecoflex, to obtain a cured model; immersing the cured model in
acetone to dissolve the ABS plastic model, to obtain a microchannel
with a gold plating on an inner wall of the microchannel in the
Ecoflex substrate; and injecting a gallium-indium eutectic into the
microchannel with a gold plating on the inner wall, inserting a
copper wire into the liquid metal at both ends of the microchannel
with a gold plating on the inner wall, and applying Ecoflex to a
port of the microchannel with a gold plating on the inner wall and
curing Ecoflex such that the circuit is encapsulated, to obtain the
liquid metal-based flexible electronic device.
[0042] FIG. 1 shows a flowchart of the method for preparing the
liquid metal-based flexible electron device according to one
embodiment of the present disclosure.
[0043] According to the circuit pattern, the ABS plastic model is
prepared by 3D printing. In the present disclosure, there is no
special limitation on the specification of the ABS plastic model.
In some embodiments, it is designed according to the required
circuit pattern. In the present disclosure, there is no special
limitation on the specific means for the 3D printing, as long as an
ABS plastic model could be obtained.
[0044] After obtaining the ABS plastic model, according to the
present disclosure, an ion sputtering is performed on the surface
of the ABS plastic model to form a gold film, to obtain a
gold-plated ABS circuit. In the disclosure, the gold film is to
improve the wettability of the gallium-indium eutectic in the
microchannel, thereby facilitating the fabrication of the
circuit.
[0045] In some embodiments of the present disclosure, the ion
sputtering is performed for 60-100 seconds.
[0046] According to the present disclosure, Ecoflex is introduced
into a mold, and then the gold-plated ABS circuit is suspended
inside the mold such that the gold-plated ABS circuit does not
contact the mold. Ecoflex is cured, to obtain a cured model. In
some embodiments of the present disclosure, the Ecoflex is a
commercial commodity produced by Smooth-On factory in the United
States. In some embodiments of the present disclosure, the mold is
made of polylactic acid (PLA).
[0047] In the present disclosure, suspending the gold-plated ABS
circuit is to ensure that the gold-plated ABS circuit is completely
covered by Ecoflex.
[0048] In some embodiments of the present disclosure, curing
Ecoflex is performed for 2-4 hours. In the present disclosure,
there is no special limitation on the specific means for curing,
and specifically, it may be cured by standing at room
temperature.
[0049] After obtaining the cured model, according to the present
disclosure, the cured model is immersed in acetone to dissolve the
ABS plastic model, to obtain a microchannel with a gold plating on
an inner wall of the microchannel in the Ecoflex substrate.
[0050] In some embodiments of the present disclosure, immersing the
cured model in acetone is performed for 12-24 hours.
[0051] In some embodiments of the present disclosure, dissolving
the ABS plastic model is performed under an ultrasonic
condition.
[0052] After obtaining the microchannel with a gold plating on the
inner wall, according to the present disclosure, a gallium-indium
eutectic is injected into the microchannel with a gold plating on
the inner wall, and then a copper wire is inserted into the liquid
metal at both ends of the microchannel with a gold plating on the
inner wall. Ecoflex is then applied to a port of the microchannel
with a gold plating on the inner wall, and cured such that the
circuit is encapsulated, to obtain the liquid metal-based flexible
electron device.
[0053] In some embodiments of the present disclosure, the
gallium-indium eutectic has a GA content of 74.5 wt %, and an In
content of 25.5 wt %. In some embodiments of the present
disclosure, the gallium-indium eutectic is extracted by using a
syringe and injected inward from one end of the microchannel.
[0054] In the present disclosure, the copper conductor has a length
of 50-70 mm, and preferably 60 mm.
[0055] In the present disclosure, there is no special limitation on
the amount of the Ecoflex to be applied, as long as the
microchannel with a gold plating on the inner wall could be
encapsulated. In some embodiments of the present disclosure, curing
the applied Ecoflex is performed for 2-4 hours. In the present
disclosure, there is no special limitation on the specific means
for curing, and specifically, it may be cured by standing at room
temperature.
[0056] The present disclosure also provides a liquid metal-based
flexible electron device as prepared by the method according to the
above technical solutions. In the present disclosure, the gold film
is transferred from the surface of ABS to the surface of the
flexible Ecoflex substrate, which improves the wettability of
liquid metal within the microchannel, thereby facilitating the
subsequent liquid metal-injection operation. The prepared flexible
liquid metal circuit has high elasticity, and could meet the needs
of various deformations, and has stable electrical performance
during service.
[0057] The present disclosure also provides use of the liquid
metal-based flexible electronic device as described in the above
technical solutions in the fields of intelligent furniture,
intelligent wear, electronic skin, flexible sensing, radio
frequency antenna, biomedicine, and aerospace. In the present
disclosure, there is no special limitation on the specific means of
the use, and any means well known to those skilled in the art may
be adopted.
[0058] In order to further illustrate the present disclosure, the
liquid metal-based flexible electron device according to the
present disclosure, a preparation method and use thereof are
described in detail below in conjunction with examples, but they
could not be understood as limiting the scope of the present
disclosure.
EXAMPLE 1
[0059] A circuit pattern was drawn by using the relevant software
in the computer, and the ABS plastic model was printed with a 3D
printer. The printed ABS plastic model was placed in an ion
sputtering instrument and an ion sputtering was performed for 60
seconds. A layer of gold film was plated on its surface. Ecoflex
was introduced into a mold, and then the gold-plated ABS circuit
was suspended inside the mold. They were stood at room temperature
for 2 hours, to be cured. The cured model (including cured Ecoflex
and ABS model) was immersed in an acetone solution for 12 hours,
and the ABS model was dissolved in acetone, After ABS was
completely dissolved, Ecoflex was taken from the acetone solution,
and rinsed, to obtain a microchannel with a gold plating on the
inner wall in the Ecoflex substrate. A gallium-indium eutectic
(EGaIn consists of 74.5 wt % of Ga and 25.5 wt % of In) was
extracted by using a syringe and injected inward from one end of
the microchannel. A copper wire having a length of 60 mm was taken
and inserted into the liquid metal at both ends of the
microchannel. Ecoflex was dropped to a port of the microchannel and
cured such that the circuit was encapsulated, obtaining a liquid
metal-based flexible electronic device.
Comparative Example Without a Gold Plating
[0060] In the comparative example, the method was the same as that
of Example 1, except that the ABS plastic model was not plated with
a gold film.
[0061] The shapes and structures of the liquid metal-based flexible
electronic devices obtained in Example 1 and the Comparative
Example are shown in FIGS. 2A-2B. It shows a dumbbell-shaped
standard tensile part, with a small middle and large ends. The
narrowest portion of the sample 203 has a length of 20 mm as shown
in FIG. 2A. The cross-sectional shape shown in
[0062] FIG. 2B is a square with side lengths 205 and 207 of 5 mm,
and there are circular microchannels with five contemplated
different sizes 209 in the middle, i.e. 0.4 mm, 0.6 mm, 0.8 mm, 1.0
mm, and 1.2 mm. The microchannel 201 filled with EGaIn liquid metal
constitutes the circuit.
[0063] The prepared liquid metal-based flexible electronic devices
were subjected to two tensile ultimate tests. In the first test,
the liquid metal-based flexible electronic devices with five
different sizes prepared in Example 1 were placed on a stepping
platform and subjected to a 1000-time tensile cycle test with a
strain of 100%. The variation curves of resistance during the cycle
are shown in FIG. 3. As shown in FIG. 3, the peak represents the
circuit resistance measured when the circuit is stretched to a
strain of 100%, and the trough represents the circuit resistance
measured when the circuit returns to its original length. After
1,000 cycles, the peaks and troughs of these circuits with five
different microchannel sizes are still very stable. All of them
have passed through the test completely. It indicates that the
circuit made by the template method could withstand the tensile
cycle with a low strain, and thus the circuit could be applicable
to a low-strain tensile application in daily life. In the second
ultimate test, the circuits with a microchannel size of 1.0 mm and
1.2 mm were subjected to a resistance test under cyclic tensile
with a strain of 600%, each microchannel size with two cases: with
a gold plating on the inner wall and without a gold plating on the
inner wall. The resistance curves under tensile are shown in FIGS.
4A-4B, and FIG. 4A represents the case without a gold plating, i.e.
the Comparative Example, and FIG. 4B represents the case with a
gold plating, i.e. Example 1. The circuits of both sizes in the
case without a gold plating have only achieved 13 cycles, while
circuits 1.0 mm in size with a gold plating have achieved 31
cycles, and circuits 1.2 mm in size with a gold plating have
achieved 26 cycles, which is at least twice than the former without
a gold plating, indicating that the gold plating on the inner wall
of the microchannel could significantly improve the stability of
the circuit and could withstand more cycles of stretching with a
higher strain.
[0064] The liquid metal-based flexible electronic devices prepared
in Example 1 were subjected to a resistance test under cyclic
tensile from a low strain to a high strain, in which the sizes of
the microchannels were 0.4 mm, 0.6 mm, 0.8 mm, 1.0 mm, and 1.2 mm,
and the range of the strain was set to 10%, 20%, 30%, 50%, 70%,
100%, 150%, 200%, 300%, 400%, 500% and 600%, 10 cycles of
stretching for each strain. The variation curve of the measured
resistance during the stretching versus time is shown in FIGS.
5A-5E, FIG. 5A for 0.4 mm; FIG. 5B for 0.6 mm; FIG. 5C for 0.8 mm;
FIG. 5D for 1.0 mm; FIG. 5E for 1.2 mm. It can be seen from FIGS.
5A-5E that circuits with microchannels 0.6 mm, 0.8 mm, 1.0 mm, and
1.2 mm in size completely passed through the cycle test without the
occurrence of any open circuit, and both of the peaks and troughs
of the circuits are stable at low strain or high strain. However,
for the circuit which is 0.4 mm in size, the cycle is ended at
about 600 s when the strain reaches 200%, and the resistance tends
to infinity, that is to say, an open circuit occurs. This should be
because the stability decreases due to a smaller size of the
circuit. The EGaIn in the microchannel is squeezed and pushed by
the Ecoflex substrate of the circuit during the multi-time cyclic
stretching, so that the distribution of EGaIn is no longer uniform,
low content in some areas and high content in another areas.
Finally, when the circuit is stretched to a large deformation, the
cross-sectional area of the microchannel also decreases rapidly.
Thus, the continuous state of EGaIn liquid metal is broken at the
place where its content is low, and the connection could not be
maintained, eventually resulting in an open circuit. For circuits
with a microchannel in a larger size, because of a larger volume of
EGaIn liquid metal inside, even if a large deformation occurs, the
squeezing of the EGaIn by the substrate would not be able to break
it, and thus an open circuit would not occur.
[0065] The peak resistance for each strain was summarized. The
summarized data was fitted from the initial value of the circuit
according to the above derived formula to obtain a summary of the
fitted curve and actual peak values, as shown in FIG. 6. From FIG.
6, it can be seen that the actual resistances measured for five
microchannel sizes are in good agreement with the curve fitted
according to the formula, and basically all points fall on the
curve. This proves that the experimental results are basically
consistent with the deduced theory. The circuit resistance during
the stretching varies according to the formula. Additionally, the
single stretching-recovering process for each strain in the
resistance curve under tensile for circuit having a microchannel
1.2 mm in size was statistically observed, as shown in FIG. 7. From
FIG. 7, it can be seen that the curves of circuit resistance under
tensile for strains ranging from 10% to 600% basically overlap, and
the tensile and recovery processes for each strain are basically
symmetrical. This also shows that the circuit resistance changes
stably and changes in conformation with the deduced formula.
[0066] The liquid metal-based flexible electronic devices prepared
in Example 1 were placed on models bent in different angles and
subjected to a resistance measurement with a multimeter, in which
the angles were 0.degree., 30.degree., 60.degree., 90.degree.,
120.degree., 150.degree. and 180.degree.. The results are shown in
FIG. 8. From FIG. 8, it can be seen that as the bending angle of
the circuit increases from 0.degree. to 180.degree., the circuit
resistance is also increasing. However, for microchannels with
different sizes, and the increase in resistance also varies. For
the circuit with a microchannel 0.4 mm in size, the resistance
increased from 135 m.OMEGA. at 0.degree. to 167 m.OMEGA. at
180.degree., while for the circuit with a microchannel 1.2 mm in
size, the resistance only increased from 10 m.OMEGA. to 14
m.OMEGA., indicating that the increase in resistance is larger when
the size of the microchannel is smaller. The stretching of Ecoflex
during bending also causes EGaIn liquid metal in the microchannel
to be stretched, thereby increasing the resistance. Further, when
the microchannel is in a smaller size, the same bending angle would
have a greater impact on the circuit. Therefore, circuits with
different microchannel sizes could be applied to different
applications as needed.
[0067] The liquid metal-based flexible electronic devices prepared
in Example 1 were placed on a fixture and twisted, in which the
twisting angles .theta. are 0.degree., 30.degree., 60.degree.,
90.degree. . . . 330.degree. and 360.degree., respectively. The
resistances of circuits were measured with a multimeter. The
results are shown in FIG. 9. From FIG. 9, it can be seen that the
resistances of circuits increase as the twisting angle of the
circuit increases from 0.degree. to 360.degree., and that the
curves are almost linear. However, for the microchannels of
different sizes, the increases in the resistance vary. The
resistance of circuit with a microchannel 0.4 mm in size increases
from 127 m.OMEGA. at 0.degree. to 147 m.OMEGA. at 360.degree.,
while the resistance of circuit with a microchannel 1.2 mm in size
only increases from 10 m.OMEGA. to 12 m.OMEGA., which is consistent
with the situation of bending, i.e. the increase in resistance is
larger when the size of the microchannel is smaller. However, the
increase when twisting is much less than the increase when bending.
When the substrate Ecoflex silicone of the circuit is twisted, the
microchannel twists and squeezes the EGaIn liquid metal inside,
thereby reducing the cross-sectional area, and thus the resistance
is increased. Further, when the microchannel is in a smaller size,
it has a higher sensitivity to this deformation, and thus the
change of the resistance is greater. The slope of the curve in the
figure was further analyzed, and summarized in FIG. 10. It can be
seen from FIG. 10 that when the microchannel is in a smaller size,
the torsion slope of the resistance is larger, indicating that the
circuit resistance is more sensitive to torsional deformation, that
is to say, it has a higher sensitivity.
[0068] When the liquid metal-based flexible electronic devices
prepared in Example 1 were pressed, the performance of the circuit
was tested, and the sensitivity was measured. As shown in FIG. 11,
the test process was as follows: weights of different masses were
placed on the EGaIn liquid metal-based flexible circuits in turn,
wherein the masses were 1 g, 2 g, 5 g, 10 g, 20 g . . . 100 g and
200 g, etc., respectively, and the microchannels in the circuits
were set as 0.4 mm, 0.6 mm, 0.8 mm, 1.0 mm and 1.2 mm in size, and
were set to form three patterns, i.e. simple pattern (the total
length of the microchannel was 70 mm), complex pattern (the total
length of the microchannel was 110 mm) and more complex pattern
(the total length of the microchannel was 170 mm), as shown in
FIGS. 12A-12C. For the three patterns, the lengths of the
microchannels per unit area of the pressed part were 7.2
mm/cm.sup.2, 13.6 mm/cm.sup.2, and 23.2 mm/cm.sup.2 respectively.
Meanwhile, considering that the thickness of the Ecoflex layer
wrapping EGaIn liquid metal may also affect the performance of the
circuit, the thicknesses of Ecoflex were also set as 0.4 mm, 0.7 mm
and 1.0 mm respectively. Classified according to the complexity of
the circuit patterns, the changes in the circuit resistances with
five microchannel sizes and different Ecoflex thicknesses with the
increase in mass of weights were finally measured, as shown in
FIGS. 13A to 15C. The experimental results show that the
resistances of circuits with three different levels of complexity,
five microchannel sizes and different Ecoflex thicknesses all
increase with the increase in mass of the weights, and that with
the same Ecoflex thickness, for the circuit with a smaller
microchannel size, the increase in the resistance thereof as the
increase in mass of the weights is greater. When the weight(s) is
placed on the EGaIn-based flexible circuit with Ecoflex as
substrate, because of gravity, the weight(s) squeezes Ecoflex and
Ecoflex deforms, accompanying with the deformation of microchannel
inside and a decrease in the cross-sectional area thereof, and the
accompanying deformation of EGaIn liquid metal encapsulated therein
because of good shaping ability of the EGaIn liquid metal.
Therefore, the resistance of the entire circuit also increases, and
when the microchannel is in a smaller size, the change of
resistance caused by the cross-sectional area deformation is
greater, and thus the change of the resistance is greater.
[0069] The liquid metal-based flexible electronic devices prepared
in Example 1 were used as a switch for controlling the light and
dark of the bulb, and a complete closed circuit was constructed, to
estimate its great role in regulating the current in the circuit.
The results are shown in FIG. 16. The EGaIn liquid metal is
equivalent to a sliding rheostat, the resistance of the EGaIn
liquid metal increases when it is stretched, so that the current in
the circuit decreases, and the voltage across the bulb decreases,
so the luminous brightness decreases. It can be seen that when the
microchannel is in a smaller size, the brightness change of the
bulb is more significant. When the circuit with a microchannel 0.4
mm in size is stretched from a strain of 0 to a strain of 300%, the
bulb becomes dark and almost extinguishes, while when the circuit
with a microchannel 1.2 mm in size is stretched to a strain of
300%, the brightness is only slightly weakened. Meanwhile, this
also illustrates from the side that the circuit with a microchannel
in a larger size could resist the influence of deformation on the
circuit, thereby improving the stability of the circuit.
[0070] The liquid metal-based flexible electronic devices prepared
in Example 1 were folded 180.degree. and twisted 360.degree., and
the changes in the brightness of the small bulb during the bending
and twisting were observed again. The results are shown in FIG. 17.
From FIG. 17, it can be seen that there is almost no changes in
brightness of the bulb. According to the above experimental data
from the bending and twisting experiments of the circuit, the
bending could at most cause an increase of about 30 m.OMEGA. in the
circuit resistance, while it is much less for the twisting, only 20
m.OMEGA., which is of a different order of magnitude from that
during the stretching and completely incomparable to that during
the stretching. Therefore, the voltage across the bulb is less
affected by the twisting so that there is almost no change in the
brightness of the bulb. This also shows that the circuit could
withstand small deformations such as bending or twisting, and
exhibits stability to a certain degree.
[0071] The liquid metal-based flexible electronic devices prepared
in Example 1 were used for the measurement of human pulse. During
the measurement, the samples were placed on a person's wrist and
held down, and meanwhile the circuit resistance is measured with a
multimeter. EGaIn liquid metal encapsulated by Ecoflex was squeezed
by the pulse beating, and deformed, and the resistance also changed
accordingly, thereby measuring the pulse. The pulse of a volunteer
in a calm state before exercise was measured, and then his pulse
after one minute of vigorous exercise was measured. The results are
shown in FIGS. 18A-18B. In a calm state before exercise, the pulse
is 72 beats/min, and one minute after the vigorous exercise, the
pulse is 112 beats/min, both of which are within the normal range
of the human pulse. It can also be seen that the pulse beating
before exercise is gentle, and the amplitude of the curve is about
1 m.OMEGA., while the human body pulse beats violently after
exercise, and the the amplitude of the curve is about 4 m.OMEGA.,
which is consistent with the actual situation.
[0072] The adhesion work of the microchannels at different stages
was calculated according to the Young-Dupre equation. The adhesion
work after plating gold was increased from 110 mJ/m.sup.2 (before
plating gold) to 200 mJ/m.sup.2, which increased by nearly 2 times.
Therefore, the wettability was significantly improved. In summary,
the obtained liquid metal-based flexible electronic devices could
be stretched to a strain of 600%, bent 180.degree., and twisted
360.degree., and when being subjected to 1,000-cycle tensile tests
with a strain of 100%, exhibit stable peaks and valleys in the
resistance curve.
[0073] It should be apparent, however, to those skilled in the art
that many more modifications besides those already described are
possible without departing from the inventive concepts herein. The
inventive subject matter, therefore, is not to be restricted except
in the spirit of the disclosure. Moreover, in interpreting the
disclosure all terms should be interpreted in the broadest possible
manner consistent with the context. In particular the terms
"comprises" and "comprising" should be interpreted as referring to
the elements, components, or steps in a non-exclusive manner,
indicating that the referenced elements, components, or steps can
be present, or utilized, or combined with other elements,
components, or steps that are not expressly referenced.
* * * * *